The effects of land use on leaf-litter processing by macroinvertebrates in an Australian temperate coastal stream

Abstract

Replacement of riparian vegetation by pasture has occurred worldwide and is predicted to have strong effects on macroinvertebrate community structure and function in streams, but this has rarely been examined. In this study, leaf processing and macroinvertebrate community structure were examined in a single stream using experimental leaf-packs and surveys of natural leaf-packs. Two sites in each of three land use categories were selected to represent reaches in forest, pasture and forest-pasture boundary regions. In two experiments using tethered leaf-packs, no differences were found in mean leaf breakdown between land use types. However, shredding invertebrates were absent from the pasture sites, so leaf breakdown in pasture resulted from chemical, physical and microbial processes only. Amounts of fine particulate organic matter in experimental leaf-packs were higher in pasture reaches than the forest and boundary reaches but did not influence leaf breakdown. Macroinvertebrate species richness did not differ between land uses. A predictive model developed for species richness and total abundance enabled direct comparison of assemblages on experimental packs to natural leaf-packs. In the forest reach and at the forest-pasture boundary, macroinvertebrate species richness and total abundance increased proportionally with the number of leaves within a pack, but this relationship was not observed in the pasture reach. Pasture land use on Skenes Creek was therefore associated with weakened relationships between allochthonous inputs and macroinvertebrate communities, but this did not alter leaf breakdown.